Device for reproduction of instantaneous occurrences



p 1940- w. FLECHSIG 2,213,761

DEVICE FOR REPRODUCTION OF INSTANTANEOUS OCCURRENCES Filed Aug. 14, 1937 Patented Sept. 3, 1940 DEVICE FOR REPRODUCTION OF INSTAN- TANEOUS OCCURRENCES Werner Flechsig,

Berlin- Charlottenburg,

Ger-

many, assignor to the firm of Fernseh Aktien- Gesellschaft, Zehlendorf, near Berlin, Germany Application August 14, 1937, Serial No. 159,185 In Germany September 22, 1936 Claims.

This invention relates to the permanent or fleeting visible reproduction of transient occurrences. It is frequently desirable to observe oscillograms of transient effects during a relatively 5 long time, or to record visibly a single phase of a rapid motion of an object for a longer period immediately after the motion is made, or finally, to extend the instantaneous efiect of a television I picture signal for one picture element over a period of time in the order of the frame period,

for the purposes of television transmission or reception.

It is the object of the present invention to provide a new and improved recording and transmitting means.

It is a known fact that a metal plate which is covered by a thin insulating layer, provided with a coating of electro-positive material, emits electrons over a long period after an excitation by an electron bombardment has ceased. This has been proven with an aluminum plate electrolytically oxidized andtreated with caesium. This phenomenon is explained by the creation of strong electrostatic fields in the thin insulating layer.

According to the present invention there is provided an envelope containing such a thin film cold emission plate adapted to be impacted by an exciting electron beam produced by an electron gun within the same envelope. The cold emission from the plate is focused in image relation upon an image screen, for example a fluorescent screen, by means of an electron optical system. Such an arrangement makes it possible to render a single transient occurrence visible over a longer 5 period of time. A device of this type is also suit able as a receiver for television images if the plate I is prepared in such a manner that the cold emission decays during the period of one television picture frame.

It has been found that it is possible to influence the cold emission by illumination. This phenomenon may either be used to terminate the cold emission, or it may be used for the development of negative images in a manner which will be described below. Heating of the plate to asufficiently high temperature can also be used to terminate the cold emission. The advantage of this arrangement over known receiver tubes is that the luminescent picture screen is exposed to electron bombardment during almost the entire time of the operation of the tube so that it may be put under heavier load than in the usual method of operation where it receives a bombardment lasting only 1 microsecond and which is, therefore, very 5 intensive.

A further application lies in the field of socalled image translators. An image produced by exposing a photocathode for a short time to the light of an optical image can be held on a fluorescent screen over a period of hours. A further pos- 5 sibility of application is to pre-excite the plate by uniform bombardment with cathode rays while a localized neutralization of varying degree of the excited state takes place by means of a different kind of ray, as for instance light; ionic, or X-rays. 10

The accompanying drawing shows several preferred embodiments of the invention. Figs. 1 and 2 both show an image receivertube, Fig. 3 shows an image translator and Fig. 4 shows an image transmitting tube. 15

In Fig. l the tube l contains an electron gun 2 of a conventional construction. I The cathode ray produced by the electron gun is sharply focused by means of a focusing lens it and is deflected over the areaof a composite plate 6 by means of the de- 20 fleeting systems t and 5. The plate ii consists of a thin aluminum layer, the surface of which is electrolytically oxidized. The oxide layer is indicated by the dotted line 1. Furthermore, the oxide layer is treated with an electro-positivc material, 25 for example caesium, which is indicated by the waved line 3. The tube also contains a fluorescent screen 9 which is disposed opposite to the plate 6. The cold emission emitted by the plate is focused upon the fluorescent screen 9 by means of an elec- 30 tron optical lens it which is preferably a long coil. According to Fig. 1 the bombardment of the plate occurs on the same side of the plate 6 from which the cold emission is emitted. In Fig. 2 the aluminum portion of the composite plate 6 is 35 made so thin that it is permeable for the exciting bombardment impacting this side of the plate. The cold emission, however, occurs on the other side, wherefore that the plate is disposed between the electron gun and a fluorescent screen 9. In 40 order to terminate the cold emission during the television picture retrace time for movingpictures the plate is either exposed to light for a very short time between two pictures, or the light generated by the fluorescent screen is partly allowed to fall 45 back upon the plate so that the cold emission is made to'decay, by virtue of the illumination generated by it, within a desired time interval. For this purpose it is also possible to heat the plate either by resistance or induction heat. 5

The image translator of Fig. 3 contains aphotocathode H, a composite plate 6 with the layers 1 and 8, and a fluorescent screen 9. An electron optical system l2 serves to focus the emission of the photocathode ll upon the plate 6 and to focus the cold emission upon the fluorescent screen 9. The plate 6 is held at a potential intermediate those of the photocathode and the fluorescent screen. The plate is preferably made in such a manner that it is permeablefor the exciting photoelectrons but still not translucent. On one side of the photocathode I I there is a dark chamber l3 with an optical objective I4 and a shutter l5, as is common in photographic cameras. If the photocathode is exposed to the light of an optical image for a short time by operating the shutter, the plate 6 is excited to produce cold emission and an imageis generated upon the fluorescent screen 9, which stays just as long as the cold emission lasts. Optical regeneration does not take place because the plate 6 is not transparent. In order to prevent the light from the fluorescent screen 9 from terminating the cold emission prior to the desired instant, it is advisable to use a luminescent material, the light of which embraces such a spectral range that the cold emission is not influenced thereby.

In a modified arrangement the photocathode is also provided with fluorescent properties and the electron optical system can be reversed by a change of potentials. In this case the optical image is projected upon the photocathode for a short time and the photoemission is focused upon the composite plate. The potentials are then changed so that the element previously functioning as the cathode now functions as the anode and the cold emission is focused by the electron optical system upon the photoelectric surface from which the photoelectrons were emitted, and there produces a visible image, due to the fact that this surface is also fluorescent.

The television picture signal transmitting tube shown in Fig. 4 contains an electron source It, for example a thermionic cathode, the emission from which uniformly floods the composite plate 6. The cold emission is then uniform over the entire area of the plate 6. By exposing the side of the plate 6 facing the optical system I! to light, the cold emission is locally decreased to varying degrees in accordance with the light intensity of the corresponding picture elements and the plate 6 emits only from those spots upon which no or very little light has fallen. The emission from the plate 6 is then focused in the plane of the stationary target l8 and is deflected across this target by means of the deflecting systems l9 and 20, so that a picture signal can be taken from the signal lead 2| of the target.

I claim:

1. A cathode ray device comprising an evacuated envelope containing an electron gun and a fluorescent plate, a cold cathode positioned to receive electrons from said gun and to direct emission to said fluorescent plate, said cold cathode comprising a conducting plate having a thin nonconducting surface on the side thereof disposed toward said electron gun, and having a secondarily emissive layer disposed on said thin nonconducting surface.

2. A cathode ray device comprising an evacuated envelope having therein an electron gun and a fluorescent plate, a cold cathode disposed between said gun and said fluorescent plate comprising a thin conductive layer permeable to elec-" trons from said gun, an insulating layer disposed upon the side of said conductive layer away from said gun, and a secondarily emissive layer disposed on said insulating layer on the side thereof away from said electron gun.

3. A cathode ray device substantially as described in claim 1 having electron focusing means disposed about said envelope'between said cold cathode and said fluorescent plate. a

4. A cathode ray device substantially as described in claim 1 having electron focusing means disposed about said envelope between said cold cathode and said fluorescent screen, and havtrons from said gun and to direct emission to said plate, said cathode comprising a conducting plate having a thin non-conducting surface on one side thereof and having secondarily emissive material disposed on said thin non-conducting surface.

WERNER FLE'CHSIG. 

